Why then does fertility in women decline progressively with age?

The available evidence indicates that both the age-related decline in female fertility and the increased risk of miscarriage can be attributed to an increase in the proportion of abnormal oocytes in an aging and shrinking follicular pool.

As the number of follicles decreases, oocyte quality also decreases, primarily due to an increased lack of meiotic disjunction, resulting in an increasing rate of oocyte and embryo aneuploidy in aging women^31-34.

Genetic alterations

A wide variety of techniques have been used to study the chromosomal composition of human oocytes. The best available evidence derived from detailed cytogenetic analysis of oocytes retrieved for IVF that failed to fertilize suggests that the overall rate of oocyte aneuploidy increases with advancing maternal age^35,36.

An analysis of trophectoderm biopsies from more than 15,000 human blastocysts also showed that the rate of aneuploidy increases with age. This is true for all chromosomes and is highest for chromosomes 15, 16, 18, 19, 21, and 22³⁷. Other embryonic factors beside aneuploidy could influence the competence of euploid embryos in an age-dependent manner.

Changes in embryonic gene expression, metabolism, and epigenetic health may explain the adverse fate of some euploid embryos. For example, advanced paternal age (which is often associated with advanced maternal age) is thought to contribute to alterations in early embryonic growth through nongenetic mechanisms. Aging- induced hypomethylation at specific binding sites in the sperm genome may be a key molecular feature that modulates embryonic and offspring³⁸.

The age-related increase in aneuploidy was most pronounced for acrocentric chromosomes (where the centromere is located near one end of the chromosome, e.g., chromosome 21)³⁷ (Figure 2).

Figure 2 Variation in the number of follicles and oocytes and abnormal oocytes in relation to age(37,38). 

In summary, accumulating evidence strongly suggests that the primary cause of age-dependent fertility decline and increased incidence of miscarriage is an increasing prevalence of aneuploidy in aging oocytes as a result, at least in part, of disordered regulatory mechanisms governing meiotic spindle formation and function.

Uterine disorders

In the past it was mentioned that age did not seem to generate any significant adverse effects on the uterus. Recent findings suggest that age significantly affects endometrial gene expression and that major changes in endometrial function occur after 35 years³⁹. Using a nongenome-wide functional approach, changes in age-affected molecular processes in the endometrium have been observed, including reduced epithelial cell proliferation due to cell cycle arrest and upregulation of ciliary processes.

Likewise, the incidence of myomas is known to increase with age. And the perception of adenomyosis is that it affects older women of reproductive age. Adenomyosis and uterine fibroids, by modifying the vascular architecture, altering normal contractility and changing the production of angiogenic factors, could alter the local and distant endometrial milieu and, consequently, endometrial function. We cannot exclude that other lesser-known factors may be consistent with our findings^40-42.

However, there is still limited evidence to suggest that uterine age itself has an important impact on fertility^43-45. With increasing maternal age, there is an increased risk of a history of uterine surgery (especially cesarean sections and myomectomies) and disorders of glucose metabolism. Both of these factors have been strongly associated with an increased risk of miscarriage in a recent large prospective registry-based study^46,47. In addition, an increased risk of miscarriage is observed in patients with positive thyroid autoantibodies. The exact pathophysiological mechanism remains controversial, but it is known that euthyroid women with positive thyroid autoantibodies are older than euthyroid women with negative autoantibodies⁴⁸.

Ovarian reserve

The term ovarian reserve refers to: 1) the size and quality of follicles that her ovaries have, and 2) the ability of the ovaries to respond to exogenous gonadotropin stimulation, which are related concepts. Since the main effect of aging on a woman's reproductive potential is a decrease in the number of oocytes and an increase in oocyte aneuploidy, the concept of ovarian reserve is relevant to female reproductive aging.

Ovarian reserve testing serve two purposes: 1) to predict fertility and 2) to obtain prognostic information about the likelihood of a successful response to ovarian stimulation in women undergoing infertility treatment.

Ovarian reserve testing in this age group is in-tended to identify women with ‘diminished ovarian reserve' (DOR). It is important to emphasize that such tests cannot and do not establish a diagnosis of DOR; they only identify women who are more likely to show a poor response to gonadotropin stimulation and potentially have a lower likelihood of achieving pregnancy with treatment.

Anti-Müllerian hormone (AMH) dosing and antral follicle count at the beginning of the cycle are primarily used to determine ovarian reserve. The quality of the oocytes is predicted by the patient's age.

Ovarian reserve testing has also become a routine element of the diagnostic evaluation of infertility. Proponents of the liberal application of ovarian reserve testing argue that abnormal tests can help persuade older women to abandon plans to pursue aggressive, expensive, and probably futile treatment, and convince younger women to do the exact opposite in order to make the most of a rapidly closing window of opportunity.

Ovarian reserve tests should always be interpreted with caution. Rigid application of test results runs the risk of inappropriate recommendations for treatment, or for no treatment, and both should be avoided. An abnormal test result does not exclude the possibility of pregnancy. Except perhaps when very abnormal, test results should not be used to deny treatment, but only to obtain prognostic information that can help guide the choice of treatment and the best use of available resources. Although the chance of pregnancy may be low, many individuals with abnormal test results will achieve pregnancy if given the opportunity. Ultimately, regardless of the prognosis, the success rate for any woman will be 0% or 100%.

Indications for ivf with own oocytes in women over 40 years old

Older age presents additional challenges and considerations compared to younger women. The main objective is to achieve a euploid embryo, i.e., a healthy baby.

1. Decrease the search time: achieving pregnancy unaided or with low complexity procedures generates very low success rates. Therefore, it should be proposed to start IVF as soon as possible.

2.Genetic counseling: in order to reduce the miscarriage rate, it is acceptable to perform a genetic study on the embryos in order to rule out aneuploidies (PGT-a).

3.Consider patients ideally under 44 years of age because the newborn rate (NB) is 2%.

4.Evaluation of the ovarian reserve and that it is within acceptable ranges, considering mainly the AMH and the antral follicle count.

5.Realistic expectations: desire to attempt IVF procedures despite knowing the low results. Recognize and accept the possibility of obtaining a reservoir of embryos.

6.Finally, sign a special informed consent oriented to the patients over 40 years of age point ing out the live birth rates (LBR) offered by the center itself.

Ovarian stimulation in women over 40 years old

The dose to be administered for stimulation depends on the ovarian reserve. If this is adequate, full doses should be administered.

On the contrary, if the ovarian reserve is diminished (2-3 antral follicles), it is suggested that the stimulation be minimal and consider performing multiple cycles, with the objective of having at least 3 embryos to send for preimplantation genetic test (PGT); this procedure is called embryo accumulation and/or banking.

We present a group of patients from the Institute of Reproductive Medicine of the Ricardo Palma Clinic who performed banking⁴⁹ (Figure 3).

Figure 3 Number oF consecutiVe cycles of ovarian stimulation per patient ≥ 40 years old for accumulation of embryos for PGT between 2017-2022 at the Ricardo Palma Clinical reproductive medicine institute. 

The accumulation of embryos proposed in this group of patients in order to increase the possibilities of having euploid embryos and the chance of a transfer was also analyzed by our group. In Figure 3 we present the number of consecutive cycles of hormonal stimulation performed in some patients. A first cycle of ART was performed in 510 patients; of these, 173 had a second cycle, 57 a third cycle, 23 a fourth cycle, and so on to 1 patient who completed 9 cycles. With each new cycle, an increase in the average number of fertilized oocytes is observed. However, the average number of blastocysts and euploid blastocysts does not increase at the same rate.

Outcome of fresh and frozen IVF and ICSI cycles with own oocytes by woman's age and number of embryos transferred

In 2020, there were 39,418 fresh IVF/ICSI cycles initiated, but as reported in Figure 5, after discarding canceled cycles, frozen cycles, and other conditions preventing embryo transfer reduced the number of cycles in which at least one mature oocyte was collected to 17,253. In addition, after discarding cases with failed fertilization, no embryo development and PGT cases without normal embryos, the number of transfer cycles was further reduced to 11,101. Table 1 provides the clinical pregnancy rates (CPR) and delivery rates per obtained oocyte and embryo transfer according to the age of the woman and the type of fertilization process.

Figure 5 Events affecting the evolution of fresh IVF/ICSI, frozen or fresh oocyte donation, frozen embryo transfer in latin america 2020. ted = thawed embryo transfer. fresh = cycles initiated with own oocytes for iVf/icsi. pGt = preimplantation Genetic study (pGt-a, pGt-m, pGt-sr reported toGether)⁵⁰. 

Table 1 Clinical pregnancy rate (cpr) and deliVery rate in Fresh iVF and icsi cycles with own oocytes according to age oF the woman, in 2020⁵⁰. 

CPR = clinical pregnancy rate; ICSI = intracytoplasmatic sperm injection

In the REDLARA report, as in previous years, ICSI accounts for 84.8% of transfers. This high proportion of ICSI with no clear explanation beyond fear of fertilization failure has remained stable in the last decade, 85.7% in the 2010 report. When stratified by age of the female partner, the pregnancy rate per oocyte retrieved was significantly higher in IVF than in ICSI only in women ≥ 35 years old (p < 0.0001). However, there was no difference in the delivery rate per oocytes retrieved and the delivery rate per embryo transfer. As expected, the chances of achieving a delivery decreased with age.

The rates differed when transferring 1 embryo or 2 embryos; or when transfering 1 embryo only having others, i.e., choosing the best one, compared to when it is the only embryo, i.e., no more embryos are available. Generally, in wom en ≥ 40, only 1 embryo is available.

In REDLARA, the proportion of blastocyst stage embryos transferred over dividing embryos increases year after year. This proportion represented 30.3% of all transfers in 2016, increasing to 77.6% in 2020. And, as mentioned above, in CPR cases it accounted for 86.8% of all transfers compared to 53.3% in fresh IVF/ICSI. When comparing the delivery rate and multiple birth rate after elective 8-cell splitting embryo transfer (day 3) and elective day 5 blastocyst transfer in IVF and ICSI cycles, the delivery rates were significantly higher after blastocyst transfer.

Influence of PGT on the TRA outcome

Over the past 5 years, the proportion of aspirations leading to PGT has increased nearly 2.5fold across all age categories (Figure 6). In 2020, a total of 144/188 centers (76.6%) reported 8,920 aspirations from fresh cycles with own oocytes where PGT was performed. This corresponds to 24.1% of aspirations with at least one mature oocyte. When stratified by age, the percentage of aspirations with PGT was 12.9% in women aged ≤ 34 years, 23.7% in women aged 35-39 years, and 33.4% in women aged ≥ 40 years.

Figure 6 5-year trend in the use of preimplantation Genetic study (PGT) in Fresh cycles oF own oocytes in aspirations oF at least 1 mature oocyte in different age groups in Latin America,2016-2020⁵⁰. 

The mean age of women who underwent PGT with their own oocytes was 38.3 (SD 3.97) and the age distribution included 17.6% in women aged ≤ 34 years, 20.2% in women aged 35-37 years, 19.7% in women 38-39 years and 42.5% in women ≥ 40 years.

The effect of PGT on the rate of delivery and miscarriage can be seen in Table 2. When stratified by age, PGT significantly decreased the miscarriage rate in all age categories, including women ≤ 34 years (p = 0.041) and women with oocyte donation (p = 0.002). Regarding the effect of PGT on the probability of achieving birth, the differences in births with and without PGT are again significantly greater with PGT in all age groups, including egg donation (p < 0.001).

Table 2 eFFect oF pgt on deliVery and miscarriage rate depending on the woman’s age in thawed egg transFer (ted) with own oocytes and ted with donated oocytes (2020)⁵⁰. 

FET = forzen embryo transfer; OD FET = Oocyte donation frozen embryon transfer; PGT = preimplantation genetic testing; PR = prevalence ratio.

^a For miscarriage the denominator is clinical pregnancies; for deliveries, the denominator is embryo transfers.

^b Likelihood of having a miscarriage. The reference group is 'with PGT'.

^c Likelihood of delivery. The reference group is 'with PGT'.

Cumulative birth rates in REDLARA were calculated in a subgroup of 4,344 women who, in addition to their fresh transfers, had frozen supernumerary embryos for subsequent transfers, regardless of whether they were used during 2020. For calculating cumulative deliveries, this latter group best reflects cumulative chances, because women without frozen embryos had their only chance after fresh transfer. The fresh transfer delivery rate is notably higher at all ages in women with frozen surplus embryos. Another interesting observation in this group of women who had surplus embryos was the less steep slope of the decline in deliveries with increasing age.

Fertility preservation

A total of 7,558 initiated cycles of fertility preservation egg vitrification were reported, of which 7,204 had at least one mature oocyte (95.3%). The age distribution of women has shown mini-mal changes in recent years and the proportion of women attempting fertility preservation at ≥38 remains very high (44.8%) (Figure 7). The mean (SD) number of vitrified oocytes in metaphase II was 7.04 (σ 5.83), with wide variations according to the age of the woman. In women ≥ 34 years old the mean was 9.02(σ 7.05), in women 35-38 years it was 7.32 (σ 5.73), in those 39-40 it was 5.77 (σ 4.52) and in women ≥ 40 it was 4.54 (σ 3.76) oocytes. In 95.1% of cases, the reason for oocyte vitrification was fertility postponement for reasons other than cancer, which represented the main reason for fertility preser vation in 4.9% of cases.

Figure 7 Fertility preserVation cycles by year according to age of Latin America women, 2017-2020. numbers include only cycles in which at least one mature oocyte was collected⁵⁰. 

Frozen embryo transfer

The proportion of TED cycles continues to increase, accounting for 66.6% of all transfers with own oocytes. This has been associated with a continued fall in the average number of fresh embryos transferred to 1.6. As reported in the past, pregnancy and delivery rates after TED were higher than after fresh transfers, regardless of the number of embryos transferred. This may seem surprising, considering that a large proportion of TED cycles are the result of failed fresh transfers. The main reason is the proportion of blastocyst-stage transfers, which is much higher in TED (86.3%) compared to only 53.6% after fresh transfers (spliting embryo). Again, this shows that it is the selection of the best blastocyst for transfer that produces the best results, either through morphology evaluation or after the addition of PGT.

The number of centers and cycles reporting PGT is increasing year after year. In 2020, 76.6% of centers reported PG from 24.1% of aspirations with at least one mature oocyte. PGT was used in 27,287 blastocysts, most of which were examined by next-generation sequencing (NGS). The proportion of aneuploidies was 49.8% of embryos in women ≤ 34 years of age, 59.9% of embryos in women between 35-39 years, and 77.1% of embryos in women ≥ 40 years. In addition, the proportion of aneuploidies in 3,166 embryos generated from oocyte donors (mean age 25.5 years) was 36.1%. As seen in Table 2, the use of PGT reduced miscarriage rates and increased delivery rates in all ages, including oocyte recipients.

Indeed, there is a benefit in using PGT to achieve greater reproductive efficiency at all ages. However, the question is whether it is cost-effective at all ages, which will depend largely on reproductive health financing policies. Regardless of a country's wealth, when most treatments are funded out-of-pocket, most consumers belong to a subgroup of middle- or high-income individuals. In this subgroup there is a triad of families with fewer children, delayed childbearing and a progressive search for certainty. The question of the absolute benefit of the PGT prevails over the trade-off between costs for the benefit sought. This partly explains the increasing use of PGT technology to ensure, as far as possible, the birth of healthy children.

Unlike previous years, the REDLARA report calculates the cumulative delivery rate for aspirations that took place only during 2020. In this cohort of 11,101 aspirations, only 4,344 (39%) had surplus embryos available for future transfer. Therefore, if cumulative births are calculated from the entire cohort, the majority of women (61%) will not have a second chance of birth from the initial aspiration cycle. This is most likely due to the high proportion (34%) of women aged 40 or older. When the cumulative delivery rate was calculated only among women who had surplus frozen embryos available for future transfers, the chance of a birth after a new transfer was already higher at all ages.

The delta generated by subsequent (cumulative) TED was also higher. Another interesting finding is the better outcome after sequential transfer of two blastocysts (1+1) compared to simultaneous transfer of two blastocysts and is best seen in women ≥ 34 years. Although the differences in delivery rates are not very large, the rate of multiple births is almost 20 times higher after simultaneous transfer of two blastocysts (1.6% vs. 30.5%, respectively) than after 1+1. The impact of multiple births in terms of perinatal mortality and preterm and extreme preterm births is multiplied by 4-9 times. In 2020, 65% of all multiple births were in women ≤ 34 years old and oocyte recipients. Therefore, a 1+1 blastocyst strategy in tese two groups should significantly reduce multiple births while maintaining acceptable delivery rates.